The importance of the uterine cervix during premature labor, labor induction and spontaneous parturition has become increasingly apparent. While some biochemical and histological changes of the cervix have been documented, the control mechanisms for changes in the physical characteritics of the cervix at parturition remain poorly defined. Such information could contribute substantially to the prevention of prematurity and to the success of labor induction in high risk pregnancy. Using a chronically instrumented sheep model, the proposed study will examine the control mechanisms of changes in cervical compliance which have been described at parturition. In the present proposal, a chronic preparation is described in which sheep are implanted with intracervical and intrauterine balloons to measure cervical compliance and uterine contractility. In addition, maternal and fetal vascular catheters are implanted to sample blood and to administer drugs. In recent years several humoral agents have been implicated as having a role in parturition. Estrogens are known to increase at parturition and are thought to induce the coincidental increases in prostaglandins. Prostaglandins appear to play a role in stimulating uterine contractions and in softening the cervix, but their cervical effects have not been documented adequately with objective measurements. The proposed study will examine the effects of prostaglandins on cervical compliance. Relaxin and prolactin have also been shown to increase at parturition in a time frame similar to cervical changes. Vasoactive intestinal polypeptide (VIP), found abundant in the genitourinary tract and placenta, might also affect the cervix at parturition. Therefore, the proposed study will examine the effects of relaxin, prolactin and VIP on cervical compliance. The proposed study will also seek to determine whether changes in cervical compliance are a result of new protein synthesis (i.e. formation of humoral peptide or enzyme) and, therefore, blocked by protein synthesis inhibition.